High energy lithium ion secondary batteries

ABSTRACT

Lithium ion secondary batteries are described that have high total energy, energy density and specific discharge capacity upon cycling at room temperature and at a moderate discharge rate. The improved batteries are based on high loading of positive electrode materials with high energy capacity. This capability is accomplished through the development of positive electrode active materials with very high specific energy capacity that can be loaded at high density into electrodes without sacrificing performance. The high loading of the positive electrode materials in the batteries are facilitated through using a polymer binder that has an average molecular weight higher than 800,000 atomic mass unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 12/403,521 filed on Mar. 13, 2009, now U.S. Pat. No. 8,187,752to Buckley et al., entitled “High Energy Lithium Ion SecondaryBatteries,” which claims priority to U.S. provisional patent applicationSer. No. 61/124,407 filed on Apr. 16, 2008 to Buckley et al., entitled“High Energy Lithium Ion Secondary Batteries,” both of which areincorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to lithium ion secondary batteries with highenergy positive electrode materials in battery configurations thatprovide for particularly high discharge energy densities for theresulting batteries. The invention also relates to methods for formingthe high energy lithium ion secondary batteries.

BACKGROUND OF THE INVENTION

Lithium batteries are widely used in consumer electronics due to theirrelatively high energy density. Rechargeable batteries are also referredto as secondary batteries, and lithium ion secondary batteries generallyhave a negative electrode material that intercalates lithium. For somecurrent commercial batteries, the negative electrode material can begraphite, and the positive electrode material can comprise lithiumcobalt oxide (LiCoO₂). In practice, only roughly 50% of the theoreticalcapacity of the cathode can be used, e.g., roughly 140 milliamp hoursper gram (mAh/g). At least two other lithium-based cathode materials arealso currently in commercial use. These two materials are LiMn₂O₄,having a spinel structure, and LiFePO₄, having an olivine structure.These other materials have not provided any significant improvements inenergy density.

Lithium ion batteries are generally classified into two categories basedon their application. The first category involves high power battery,whereby lithium ion battery cells are designed to deliver high current(Amperes) for such applications as power tools and Hybrid ElectricVehicles. However, by design, these battery cells are lower in energysince a design providing for high current generally reduces total energythat can be delivered from the cell. The second design category involveshigh energy cells, whereby lithium ion battery cells are designed todelivery low to moderate current (Amperes) for such applications ascellular phones, lap-top computers, Electric vehicles (EVs) and Plug inHybrid electric vehicles (PHEVs) with the delivery of higher totalenergy.

SUMMARY OF THE INVENTION

In a first aspect, the invention pertains to a lithium ion secondarybattery comprising a positive electrode that comprises a positiveelectrode active material and a binder, a negative electrode thatcomprises a first lithium intercalating composition, an electrolyte thatcomprises lithium ions, and a separator between the positive electrodeand the negative electrode. In some embodiments, the battery has adischarge energy density of at least about 240 Wh/kg when dischargedfrom 4.6V to 2.0V. The positive electrode active material of thepositive electrode of the battery comprises a second lithiumintercalation composition. The positive electrode of the battery cancomprise at least about 92 weight percent of the positive electrodeactive material. The positive electrode active material comprising thesecond lithium intercalation composition that is represented by aformula of xLiMO₂.(1−x)Li₂M′O₃ where M is one or more trivalent metalion with at least one metal ion being Mn⁺³, Co⁺³, or Ni⁺³ and M′represents one or more metal ions having an average valance of +4 and0<x<1. In some embodiments, the second lithium intercalation compositioncan further comprise from about 0.1 mole percent to about 10 molepercent metal fluoride as a coating. In additional embodiments, thepositive electrode of the battery can comprise from about 0.1 to 5weight percent electrically conductive agents and about 0.5 to 7.9weight percent polymer binder that are distinct from the second lithiumintercalation composition. The binder can comprise a polymer having anaverage molecular weight of at least about 800,000 atomic mass unit. Insome embodiments, the negative electrode of the battery has a thicknessfrom about 65 microns to about 200 microns on a single side of a currentcollector. In further embodiments, the battery can have a dischargeenergy density of at least about 250 Wh/kg to 550 Wh/kg. The battery canhave a volumetric discharge energy density of at least about 550 Wh/l.

In a second aspect, the invention pertains to a lithium ion secondarybattery comprising a positive electrode, a negative electrode comprisinga first lithium intercalating composition, and a separator between thepositive electrode and the negative electrode where the positiveelectrode comprises at least about 92 weight percent positive electrodeactive material, about 0.1 to 5 weight percent electrically conductiveagents, and about 0.5 to 7.9 weight percent a polymer binder. In someembodiments, the positive electrode active material of the batterycomprises a second lithium intercalation composition represented by aformula xLiMO₂.(1−x)Li₂M′O₃ where M is one or more trivalent metal ionwith at least one metal ion being Mn⁺³, Co⁺³, or Ni⁺³ and M′ representsone or more metal ions having an average valance of +4 and 0<x<1. Anoptional fluorine dopant can optionally replace up to about 1 atomicpercent of the oxygen in the formula of the second lithium intercalationcomposition. The positive electrode of the battery has a density of atleast about 2.5 g/mL In some other embodiments, the second lithiumintercalation composition is represented by a formulaLi_(1+x)Ni_(α)Mn_(β)Co_(γ)O₂, where x ranges from about 0.05 to about0.25, α ranges from about 0.1 to about 0.4, β ranges from about 0.4 toabout 0.65, and γ ranges from about 0.05 to about 0.3. In someembodiments, the positive electrode material can further comprise fromabout 1.0 mole percent to about 10 mole percent metal fluoride as acoating. In one embodiment, the metal fluoride coating comprises AlF₃.In some embodiments, the second lithium intercalation composition of thepositive electrode active material is represented by a formulaLi_(1+x)Ni_(α)Mn_(β)Co_(γ)M″_(δ)O_(2−z/2)F_(z), where x ranges fromabout 0.05 to about 0.25, α ranges from about 0.1 to about 0.4, β rangesfrom about 0.4 to about 0.65, γ ranges from about 0.05 to about 0.3, δranges from about 0 to about 0.1 and z ranges from about 0 to about 0.1,and where M″ is Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb or combinationsthereof. The negative electrode of the battery can comprise graphite,synthetic graphite, hard carbon, graphite coated metal foil, coke or acombination thereof. In some embodiments, the separator of the batterycomprises polyethylene, polypropylene, ceramic-polymer composites, or acombination thereof. In particular, the separator can comprise apolyethylene-polypropylene-polyethylene tri-layer membrane. Also, theelectrically conductive material of the positive electrode can comprisegraphite, carbon black, metal powders, metal fibers, or a combinationthereof. In some embodiments, the polymer binder of the positiveelectrode can comprise polyvinylidine fluoride (PVDF), polyethyleneoxide, polyethylene, polypropylene, polytetrafluoroethylene,polyacrylates, ethylene-(propylene-diene monomer) copolymer (EPDM) andmixtures and copolymers thereof. With respect to the structure, thebattery can comprise a plurality of electrodes with each polarityseparated by separators within a casing. In some embodiments, theelectrodes and separators of the battery can be stacked, jelly-rolled,or folded inside the casing. In general, the casing of the batterycomprises a polymeric film, a metallic foil, a metal can, or acombination thereof. For example, the casing of the battery can beprismatic in shape or cylindrical in shape. In some embodiments, thebattery described herein has a discharge energy density of at leastabout 250 Wh/kg when discharged from 4.6V to 2.0V.

In a third aspect, the invention pertains to a method for forming alithium ion secondary battery. The method comprises assembling apositive electrode, a negative electrode, and a separator to form thebattery that has a discharge energy density of at least about 240 Wh/kg.The separator is sandwiched between the positive electrode and thenegative electrode of the battery and the positive electrode comprises abinder and a positive electrode active material comprising a lithiumintercalation composition. The density of the positive electrode is atleast about 2.5 grams per milliliter (g/mL). In some embodiments, thepositive electrode of the battery is fainted by coating the positiveelectrode active material with the binder onto a current collector. Thepositive electrode can comprise at least about 92 weight percent ofpositive electrode active material where the lithium intercalationcomposition is represented by a formula of xLiMO₂.(1−x)Li₂M′O₃ where Mis one or more trivalent metal ion with at least one metal ion beingMn⁺³, Co⁺³, or Ni⁺³ and M′ represents one or more metal ions having anaverage valance of +4 and 0<x<1. The current collector of the positiveelectrode of the battery can comprise a metal foil, a metal grid,expanded metal, or metal foam. In further embodiments, the currentcollector of the positive electrode of the battery comprises nickel,aluminum, stainless steel, copper or a combination thereof. In someembodiments, the positive electrode of the battery further comprisesfrom about 0.1 to 5 weight percent electrically conductive agents,and/or from about 0.5 to 7.9 weight percent polymer binder. The binderof the positive electrode of the battery can comprise a polymer havingan average molecular weight of at least about 800,000 atomic mass unit.In additional embodiments, the negative electrode has a thickness fromabout 65 microns to about 200 microns on a single side of a currentcollector. In some embodiments, the battery has a discharge energydensity of at least about 250 Wh/kg when discharged from 4.6V to 2.0V.

In a fourth aspect, the invention pertains to a lithium ion secondarybattery that comprises a positive electrode, a negative electrodecomprising a first lithium intercalating composition, and a separatorbetween the positive electrode and the negative electrode. The positiveelectrode can comprise at least about 92 weight percent positiveelectrode active material, about 0.1 to 5 weight percent electricallyconductive agents, and about 0.5 to 7.9 weight percent polymer bindercomprising PVDF that has an average molecular weight of at least about800,000 atomic mass unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a battery structure separated from acontainer.

FIG. 2 is a plot of first cycle charge/discharge voltage versus specificcapacities of a battery described in example 1 cycled at a dischargerate of C/10 in the voltage range of 2.0-4.6V.

FIG. 3 is a plot of specific capacity versus cycle life for the batteryof FIG. 2 showing variation of the discharge capacities as function ofcycle number.

FIG. 4 is a plot of first cycle charge/discharge voltage versus specificcapacities of a coin cell battery described in example 2 cycled at adischarge rate of C/10 in the voltage range of 2.0-4.6V.

FIG. 5 a is a photo of the front of the pouch cell battery constructedin Example 3.

FIG. 5 b is a photo of the side of the pouch cell battery constructed inExample 3.

FIG. 5 c is a discharge curve of the pouch cell battery constructed inExample 3.

DETAILED DESCRIPTION OF THE INVENTION

Lithium ion batteries with designs described herein exhibit extremelyhigh total energy as well as energy density, which are particularlysuitable for low to medium rate applications. These batteries also havegood cycling properties such that the high energy values can be usedadvantageously over a significant period of time. The improved batteriesare based in part on positive electrode materials with high energycapacity. Battery designs described herein provide for advantageouslyusing these high energy capacity positive electrode materials to achievethe extremely high energies described herein. Specifically, the batterydesigns can involve very high loadings of positive electrode activematerials. The development of synthesis approaches that achieve positiveelectrode active materials that have a high tap density providesappropriate materials for achieving the high loadings described hereinfor the positive electrodes. In addition, the very high loading of thepositive electrode active materials can be further facilitated in someembodiments at least in part through the use of a polymer binder with amolecular weight of at least about 800,000 AMU. Corresponding methods toform the battery cells are described. Furthermore, the positiveelectrode active materials can be coated, doped or a combination thereofwith an inorganic fluoride composition to improve the cycling propertiesof the cells at a high energy density. In particular, the inorganiccoatings that provide improved cycling performance can also improve orat least not significantly diminish the overall energy density of thepositive electroactive materials even though the weight of the coatingdoes not directly contribute to the capacity.

Lithium has been used in both primary and secondary batteries. Anattractive feature of lithium metal is its light weight and the factthat it is the most electropositive metal, and aspects of these featurescan be advantageously captured in lithium ion batteries also. Certainforms of metals, metal oxides, and carbon materials are known toincorporate lithium ions into its structure through intercalation orsimilar mechanisms. Desirable mixed metal oxides are described furtherherein to function as electroactive materials for positive electrodes insecondary lithium ion batteries. Lithium ion batteries refer tobatteries in which the negative electrode active material is also alithium intercalation material. If lithium metal itself is used as theanode or negative electroactive material, the resulting batterygenerally is simply referred to as a lithium battery.

The positive electrode active materials used herein comprise lithiumintercalating metal oxide compositions. In some embodiments, the lithiummetal oxide compositions can comprise lithium rich compositions thatgenerally are believed to form a layered composite structure. In someembodiments, the positive electrode of the battery can comprise at leastabout 92 weight percent of positive electrode active material, and thepositive electrode active material can comprise a compositionrepresented by a formula xLiMO₂.(1−x)Li₂M′O₃ where M is one or moretrivalent metal ion with at least one metal ion being Mn⁺³, Co⁺³, orNi⁺³ and M′ represents one or more metal ions having an average valanceof +4 and 0<x<1. This material can optionally have a fluorine dopantthat substitutes for oxygen and/or about 0.1 mole percent to about 10mole percent metal fluoride as a coating. The positive electrode of thebattery can additionally comprise about 0.1 to about 5 weight percentelectrically conductive agents and about 0.5 to about 7.9 weight percentpolymer binder.

In some embodiments, the negative electrode of the battery can have athickness from about 65 microns to about 200 microns on a single side ofa current collector. The negative electrode of the battery can comprisegraphite, synthetic graphite, hard carbon, graphite coated metal foil,coke or a combination thereof. The separator of the battery can comprisepolyethylene, polypropylene, ceramic-polymer composites, or acombination thereof. Specifically, the separator can be apolyethylene-polypropylene-polyethylene tri-layer membrane. Theelectrically conductive material of the positive electrode can comprisegraphite, carbon black, metal powders, metal fibers, or a combinationthereof.

In general, a polymer binder can be used to adhere the powder togetherin the positive electrode as an integral structure. The polymer binderof the positive electrode can comprise polyvinylidine fluoride (PVDF),polyethylene oxide, polyethylene, polypropylene,polytetrafluoroethylene, polyacrylates, ethylene-(propylene-dienemonomer) copolymer (EPDM) and mixtures and copolymers thereof. For PVDFbinders, the polymer can have a molecular weight of at least about800,000 AMU. The use of high molecular weight PVDF polymers has beenfound to provide for higher powder loadings into the positive electrodewithout adversely changing the performance of the battery whileobtaining a mechanically stable electrode. In some commercialembodiments, the batteries generally comprise a plurality of electrodesseparated by separator(s) such that the structure is stacked or rolledwithin a casing. The casing of the battery can be a polymeric film, ametallic foil, a metal can, or a combination thereof. The battery thusformed can be coin or button cell battery, cylindrical battery,prismatic battery or pouch cell battery.

The resultant battery generally can have a discharge energy density ofat least about 240 Wh/kg when discharged from 4.6V to 2.0. In someembodiments, the resultant battery can have a discharge energy densityof at least about 250 Wh/kg to 550 Wh/kg. In further embodiments, thebattery can have a volumetric discharge energy density of at least about550 Wh/l. In some embodiments, the resultant battery can have avolumetric discharge energy density of at least about 650 W11/1 to 1150Wh/l.

The batteries described herein are lithium ion batteries generally usinga non-aqueous electrolyte that comprises lithium ions. For secondarylithium ion batteries, lithium ions are released from the negativeelectrode during discharge such that the negative electrode functions asan anode during discharge with the generation of electrons from theoxidation of lithium upon its release from the electrode.Correspondingly, the positive electrode takes up lithium ions throughintercalation or the like during discharge such that the positiveelectrode functions as a cathode which neutralizes the lithium ions withthe consumption of electrons. Upon recharging of the secondary cell, theflow of lithium ions is reversed through the cell with the negativeelectrode taking up lithium and with the positive electrode releasinglithium as lithium ions.

Some of the positive electrode material compositions described hereinhave a low risk of fire for improved safety properties due to theirspecific compositions with a layered structure and reduced amounts ofnickel relative to some other high capacity cathode materials. Also,these compositions use low amounts of elements that are less desirablefrom an environmental perspective, and can be produced from startingmaterials that have reasonable cost for commercial scale production.

The word “element” is used herein in its conventional way as referringto a member of the periodic table in which the element has theappropriate oxidation state if the element is in a composition and inwhich the element is in its elemental form, M⁰, only when stated to bein an elemental form. Therefore, a metal element generally is only in ametallic state in its elemental form or a corresponding alloy of themetal's elemental form. In other words, a metal oxide or other metalcomposition, other than metal alloys, generally is not metallic.

Rechargeable batteries have a range of uses, such as mobilecommunication devices, such as phones, mobile entertainment devices,such as MP3 players and televisions, portable computers, combinations ofthese devices that are finding wide use, as well as transportationdevices, such as automobiles and fork lifts. The batteries describedherein that incorporate improved positive electrode active materialswith respect to specific capacity and cycling can provide improvedperformance for consumers, especially for medium current applications.

Positive Electroactive Materials

The improved high energy batteries described herein generallyincorporate positive electroactive materials with a large energy densityrelative to conventional materials. These materials can be prepared withsuitable material properties, for example, tap density, such that thepowders can be effectively assembled into batteries that havecorrespondingly high energies. Thus, appropriate improved positiveelectroactive materials have been discovered to be useful in producingthe desirable batteries with the assembly processes described herein.

When the corresponding batteries with the intercalation-based positiveelectrode active materials are in use, the intercalation and release oflithium ions from the lattice induces changes in the crystalline latticeof the electroactive material. As long as these changes are essentiallyreversible, the capacity of the material does not change. However, thecapacity of the active materials is observed to decrease with cycling tovarying degrees. Thus, after a number of cycles, the performance of thecell falls below acceptable values, and the cell is replaced. Also, onthe first cycle of the cell, generally there is an irreversible capacityloss that it significantly greater than per cycle capacity loss atsubsequent cycles. The irreversible capacity loss is the differencebetween the charge capacity of the new cell and the first dischargecapacity. To compensate for this first cycle irreversible capacity loss,extra electroactive material is included in the negative electrode suchthat the cell can be fully charged even though this lost capacity is notaccessible during most of the life of the cell so that negativeelectrode material is essentially wasted.

The lithium ion batteries can use a positive electrode active materialthat is lithium rich relative to a reference homogenous electroactivelithium metal oxide composition. While not wanted to be limited bytheory, it is believed that appropriately formed lithium-rich lithiummetal oxides have a composite crystal structure in which, for example, aLi₂MnO₃ is structurally integrated with either a layered LiMnO₂component or a spinel LiMn₂O₄ component or similar compositecompositions with the manganese ions substituted with other transitionmetal ions with equivalent oxidation states. In some embodiments, thepositive electrode material can be represented in two component notationas xLiMO₂.(1−x)Li₂M′O₃ where M is one or more of trivalent metal ionswith at least one ion being Mn⁺³, Co⁺³, or Ni⁺³ and where M′ is one ormore tetravalent metal ions and 0<x<1. These compositions are describedfurther in U.S. Pat. No. 6,677,082 to Thackeray et al. (the '082Patent), entitled “Lithium Metal Oxide Electrodes for Lithium Cells andBatteries” and U.S. Pat. No. 6,680,143 to Thackeray et al. (the '143Patent), entitled “Lithium Metal Oxide Electrodes for Lithium Cells andBatteries,” both of which are incorporated herein by reference. Thackeryidentified Mn, Ti and Zr as being of particular interest as M′ and Mnand Ni for M.

Batteries formed from these materials have been observed to cycle athigher voltages and with higher capacities relative to batteries formedwith corresponding LiMO₂ compositions. In other embodiments, the layeredlithium rich compositions can be represented in two component notationas x Li₂MnO₃.(1−x)LiMn_(2−y)M_(y)O₄, where M is one or more metalcations. These compositions are described further in published U.S.patent application 2006/0051673 to Johnson et al., entitled “ManganeseOxide Composite Electrodes for Lithium Batteries,” incorporated hereinby reference. The positive electrode materials with the compositecrystal structure can exhibit high specific capacity that is above 200milliamp hours per gram (mAh/g) at room temperature with good cyclingproperties.

The structure of some specific layered structures is described furtherin Thackery et al., “Comments on the structural complexity oflithium-rich Li_(1+x)M_(1−x)O₂ electrodes (M=Mn,Ni,Co) for lithiumbatteries,” Electrochemistry Communications 8 (2006), 1531-1538,incorporated herein by reference. The study reported in this articlereviewed compositions with the formulasLi_(1+x)[Mn_(0.5)Ni_(0.5)]_(1−x)O₂ andLi_(1+x)[Mn_(0.333)Ni_(0.333)Co_(0.333)]_(1−x)O₂. The article alsodescribes the structural complexity of the layered materials.

It has also been found that metal and fluorine dopants can influence thecapacity, impedance and stability of the layered lithium metal oxidestructures. These compositions with suitable metal and fluorine dopantscan similarly be used in the batteries described herein. Someembodiments of these metal and halogen atom doped, e.g., fluorine doped,compositions are described further in U.S. Pat. No. 7,205,072 to Kang etal., entitled “Layered Cathode Materials for Lithium Ion RechargeableBatteries,” incorporated herein by reference. These metal and/or halogenatom doped variations on the layered lithium metal oxide structures cansimilarly be used in the high energy batteries described herein. It hasbeen found that metal fluoride compositions can be successfully used tostabilize the cycling of high energy capacity compositions to maintain adischarge capacity of at least about 220 mAh/g for 10 or moredischarge/recharge cycles.

Positive electrode active materials with an optional fluorine dopant canbe described by the formulaLi_(1+x)Ni_(α)Mn_(β)Co_(γ)M_(δ)O_(2−z/2)F_(z), where x ranges from about0.05 to about 0.25, α ranges from about 0.1 to about 0.4, β range fromabout 0.4 to about 0.65, γ ranges from about 0.05 to about 0.3, δ rangesfrom about 0 to about 0.1 and z ranges from about 0 to about 0.1, andwhere M is Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb or combinationsthereof. The fluorine is a dopant that can contribute to cyclingstability as well as improved safety of the materials. In embodiments inwhich z=0, this formula reduces to Li_(1+x)Ni_(α)Mn_(β)Co_(γ)M_(δ)O₂. Ithas been found that suitable coatings provide desirable improvements incycling properties without the use of a fluorine dopant, although it maybe desirable to have a fluorine dopant in some embodiments. Furthermore,in some embodiments it is desirable to have δ=0 such that thecompositions are simpler while still providing improved performance. Forthese embodiments, if z=0 also, the formula simplifies toLi_(1+x)Ni_(α)Mn_(β)Co_(γ)O₂, with the parameters outlined above.Compositions represented with the formula Li_(1+x)Ni_(α)Mn_(β)Co_(γ)O₂can be alternatively written in the two component notation referencedabove. A person of ordinary skill in the art will recognize thatadditional ranges of parameter values within the explicit ranges aboveare contemplated and are within the present disclosure.

High specific capacities were obtained for thisLi_(1+x)Ni_(α)Mn_(β)Co_(γ)M_(δ)O_(2−z/2)F_(z) composition usingsynthesis approaches described in U.S. application Ser. No. 12/246,814to Venkatachalam et al. (the '814 application) entitled “PositiveElectrode Material for Lithium Ion Batteries Having a High SpecificDischarge Capacity and Processes for the Synthesis of these Materials”and U.S. application Ser. No. 12/332,735 to Lopez et al. (the '735application) entitled “Positive Electrode Material for High SpecificDischarge Capacity Lithium Ion Batteries”, both incorporated herein byreference. In particular, surprisingly good results have been obtainedfor Li[Li_(0.2)Ni_(0.175)Co_(0.10)Mn_(0.525)]O₂. A carbonateco-precipitation process described in the '735 application gave desiredlithium rich metal oxide materials having cobalt in the composition andexhibiting the high specific capacity performance with superior tapdensity. These copending patent applications also describe the effectiveuse of coatings to improve performance and cycling.

Appropriate coating materials can both improve the long term cyclingperformance of the material as well as decrease the first cycleirreversible capacity loss. While not wanting to be limited by theory,the coatings may stabilize the crystal lattice during the uptake andrelease of lithium ions so that irreversible changes in the crystallattice are reduced significantly. In particular, metal fluoridecompositions can be used as effective coatings. The general use of metalfluoride compositions as coatings for cathode active materials,specifically LiCoO₂ and LiMn₂O₄, is described in published PCTapplication WO 2006/109930A to Sun et al. (the '930 application),entitled “Cathode Active Material Coated with Fluorine Compound forLithium Secondary Batteries and Method for Preparing the Same,”incorporated herein by reference. This patent application providesresults for LiCoO₂ coated with LiF, ZnF₂ or AlF₃. It has been discoveredthat metal fluoride coatings can provide significant improvements forlithium rich layered positive electrode active materials describedherein. These improvements relate to long term cycling withsignificantly reduced degradation of capacity, a significant decrease infirst cycle irreversible capacity loss and an improvement in thecapacity generally. The amount of coating material can be selected toaccentuate the observed performance improvements.

In particular, the cycling properties of the batteries formed from themetal fluoride coated lithium metal oxide have been found tosignificantly improve from the uncoated material. Additionally, theoverall capacity of the batteries also shows desirable properties withthe fluoride coating, and the irreversible capacity loss of the firstcycle of the battery is reduced. As discussed earlier, first cycleirreversible capacity loss of a battery is the difference between thecharge capacity of the new battery and its first discharge capacity. Thebulk of the first cycle irreversible capacity loss is generallyattributed to the positive electrode material.

The coating provides an unexpected improvement in the performance of thehigh capacity lithium rich compositions used herein. In general, aselected metal fluoride or metalloid fluoride can be used for thecoating. Similarly, a coating with a combination of metal and/ormetalloid elements can be used. Metal/metalloid fluoride coatings havebeen proposed to stabilize the performance of positive electrode activematerials for lithium secondary batteries. Suitable metals and metalloidelements for the fluoride coatings include, for example, Al, Bi, Ga, Ge,In, Mg, Pb, Si, Sn, Ti, Tl, Zn, Zr and combinations thereof. Aluminumfluoride can be a desirable coating material since it has a reasonablecost and is considered environmentally benign. The metal fluoridecoating are described generally in the '930 application to Sun et al.The Sun PCT application referenced above specifically refers to thefollowing fluoride compositions, CsF, KF, LiF, NaF, RbF, TiF, AgF, AgF₂,BaF₂, CaF₂, CuF₂, CdF₂, FeF₂, HgF₂, Hg₂F₂, MnF₂, MgF₂, NiF₂, PbF₂, SnF₂,SrF₂, XeF₂, ZnF₂, AlF₃, BF₃, BiF₃, CeF₃, CrF₃, DyF₃, EuF₃, GaF₃, GdF₃,FeF₃, HoF₃, InF₃, LaF₃, LuF₃, MnF₃, NdF₃, VOF₃, PrF₃, SbF₃, ScF₃, SmF₃,TbF₃, TiF₃, TmF₃, YF₃, YbF₃, TlF₃, CeF₄, GeF₄, HfF₄, SiF₄, SnF₄, TiF₄,VF₄, ZrF₄, NbF₅, SbF₅, TaF₅, BiF₅, MoF₆, ReF₆, SF₆, and WF₆.

The effect of an AlF₃ coating on the cycling performance ofLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ is described further in an article to Sunet al., “AlF₃-Coating to Improve High Voltage Cycling Performance ofLi[Ni_(1/3)Co_(1/3)Mn_(1/3)]O₂ Cathode Materials for Lithium SecondaryBatteries,” J. of the Electrochemical Society, 154 (3), A168-A172(2007). Also, the effect of an AlF₃ coating on the cycling performanceof LiNi_(0.8)Co_(0.1)Mn_(0.1)O₂ is described further in an article toWoo et al., “Significant Improvement of Electrochemical Performance ofAlF₃-Coated Li[Ni_(0.8)Co_(0.1)Mn_(0.1)]O₂ Cathode Materials,” J. of theElectrochemical Society, 154 (11) A1005-A1009 (2007), incorporatedherein by reference. A reduction in irreversible capacity loss was notedwith Al₂O₃ coatings by Wu et al., “High Capacity, Surface-ModifiedLayered Li[Li_((1−x)/3)Mn_((2−x)/3)Ni_(x/3)Co_(x/3)]O₂ Cathodes with LowIrreversible Capacity Loss,” Electrochemical and Solid State Letters, 9(5) A221-A224 (2006), incorporated herein by reference.

It has been found that metal/metalloid fluoride coatings cansignificantly improve the performance of lithium rich layeredcompositions for lithium ion secondary batteries as demonstrated in theexamples in U.S. application Ser. No. 12/246,814 to Venkatachalam et al.(the '814 application) entitled “Positive Electrode Material for LithiumIon Batteries Having a High Specific Discharge Capacity and Processesfor the Synthesis of these Materials” and U.S. Application Ser. No.12/332,735 to Lopez et al. (the '735 application) entitled “PositiveElectrode Material for High Specific Discharge Capacity Lithium IonBatteries”, both incorporated herein by reference. The coating improvesthe capacity of the batteries. However, the coating itself is notelectrochemically active. When the loss of specific capacity due to theamount of coating added to a sample exceeds where the benefit of addingcoating is offset by its electrochemical inactivity, reduction inbattery capacity can be expected. In general, the amount of coating canbe selected to balance the beneficial stabilization resulting from thecoating with the loss of specific capacity due to the weight of thecoating material that generally does not contribute directly to a highspecific capacity of the material. In general, the amount of coatingmaterial ranges from about 0.01 mole percent to about 10 mole percent,in further embodiments from about 0.1 mole percent to about 7 molepercent, in additional embodiments from about 0.2 mole percent to about5 mole percent, and in other embodiments from about 0.5 mole percent toabout 4 mole percent. A person of ordinary skill in the art willrecognize that additional ranges of coating material within the explicitranges above are contemplated and are within the present disclosure. Theamount of AlF₃ effective in AlF₃ coated metal oxide materials to improvethe capacity of the uncoated material is related to the particle sizeand surface area of the uncoated material. In particular, a higher molepercentage of metal fluoride coating generally can be used for a highersurface area powder to achieve an equivalent effect relative to acoating on a lower surface area powder.

The positive electrode active compositions can exhibit surprisingly highspecific capacities in lithium ion cells under realistic dischargeconditions. In some embodiments based on improved synthesis approaches,the lithium rich positive electrode active materials with the compositecrystal structure can exhibit high specific capacity that is above 250mAh/g at room temperature with good cycling properties for dischargefrom 4.6 volts. In some other embodiments, the lithium rich positiveelectrode active materials with the composite crystal structure usedherein can exhibit high specific capacity that is above 235 mAh/g atroom temperature with good cycling properties for discharge from 4.6volts and high tap density above 1.8 g/mL. In general, when specificcapacities are comparable, a higher tap density of a positive electrodematerial results in a higher overall capacity of a battery. It is notedthat during charge/discharge measurements, the specific capacity of amaterial depends on the rate of discharge. The maximum capacity of aspecific cell is measured at very slow discharge rates. In actual use,the actual capacity is less than the maximum due to discharge at afinite rate. More realistic capacities can be measured using reasonablerates of discharge that are more similar to the rates during use. Forlow to moderate rate applications, a reasonable testing rate involves adischarge of the cell over three hours. In conventional notation this iswritten as C/3 or 0.33 C. The positive electrode active materials usedherein can have a specific discharge capacity of at least about 250mAh/g at a discharge rate of C/3 at the tenth discharge/charge cycle atroom temperature when discharged from 4.6 volts. In some embodiments,the positive electrode active materials used herein can have a specificdischarge capacity of at least about 250 mAh/g at a discharge rate ofC/10 at room temperature when discharged from 4.6 volts and tap densityabove 1.8 g/mL The greatest capacity performance in the lithium ionbatteries has been obtained with coated materials.

The positive electrode material can synthesized generally byco-precipitation and sol-gel processes detailed in U.S. application Ser.No. 12/246,814 to Venkatachalam et al. (the '814 application) entitled“Positive Electrode Material for Lithium Ion Batteries Having a HighSpecific Discharge Capacity and Processes for the Synthesis of theseMaterials” and U.S. application Ser. No. 12/332,735 to Lopez et al. (the'735 application) entitled “Positive Electrode Material for HighSpecific Discharge Capacity Lithium Ion Batteries”, both incorporatedherein by reference. In some embodiments, the positive electrodematerial is synthesized by precipitating a mixed metal hydroxide orcarbonate composition from a solution comprising +2 cations wherein thehydroxide or carbonate composition has a selected composition. The metalhydroxide or carbonate precipitates are then subjected to heat treatmentetc. to form a crystalline layered lithium metal oxide composition.

The lithium element can be incorporated into the material at one or moreselected steps in the process. For example, a lithium salt can beincorporated into the solution prior to or upon performing theprecipitation step through the addition of a hydrated lithium salt. Inthis approach, the lithium species is incorporated into the carbonatematerial in the same way as the other metals. Also, due to theproperties of lithium, the lithium element can be incorporated into thematerial in a solid state reaction without adversely affecting theresulting properties of the product composition. Thus, for example, anappropriate amount of lithium source generally as a powder, such asLiOH.H₂O, LiOH, Li₂CO₃, or a combination thereof, can be mixed with theprecipitated metal hydroxide or carbonate. The powder mixture is thenadvanced through the heating step(s) to form the oxide and then thecrystalline positive electrode material.

The fluoride coating of the positive electrode material can be depositedusing a solution based precipitation approach. A powder of the positiveelectrode material can be mixed in a suitable solvent, such as anaqueous solvent. A soluble composition of the desired metal/metalloidcan be dissolved in the solvent. Then, NH₄F can be gradually added tothe dispersion/solution to precipitate the metal fluoride. The totalamount of coating reactants can be selected to form the desired amountof coating, and the ratio of coating reactants can be based on thestoichiometry of the coating material. The coating mixture can be heatedduring the coating process to reasonable temperatures, such as in therange from about 60° C. to about 100° C. for aqueous solutions for fromabout 20 minutes to about 48 hours, to facilitate the coating process.After removing the coated electroactive material from the solution, thematerial can be dried and heated to temperatures generally from about250° C. to about 600° C. for about 20 minutes to about 48 hours tocomplete the formation of the coated material. The heating can beperformed under a nitrogen atmosphere or other substantially oxygen freeatmosphere.

Battery Cell Design

In the improved batteries herein, high energy positive electrodematerials described above are effectively incorporated into thebatteries to achieve extremely high performance values. In particular,the ability to synthesize high energy density electroactive materialswith a high tap density has been found to allow for positive electrodesat high active material loadings. It has also been found that highmolecular weight polymers allow for the formation of electrodes with lowamounts of polymers without compromising the mechanical stability of theelectrodes or the electrode performance. Based on these importantadvances, batteries can be formed having very high energy densities aswell as high volumetric energies.

A schematic diagram of a battery without a casing is shown in FIG. 1.Specifically a battery 100 is shown schematically having a negativeelectrode 102, a positive electrode 104 and a separator 106 betweennegative electrode 102 and positive electrode 104. A battery cancomprise multiple positive electrodes and multiple negative electrodes,such as in a stack, with appropriately placed separators. Electrolyte incontact with the electrodes provides ionic conductivity through theseparator between electrodes of opposite polarity. A battery generallycomprises current collectors 108, 110 associated respectively withnegative electrode 102 and positive electrode 104. Alternatively, theelectrodes and separators can be jelly-rolled or folded into differentconfigurations before enclosed in a casing.

Commercial cells are generally designed to have an excess capacity inthe negative electrode relative to the positive electrode so that thecells are not limited by the anode during discharge and so that lithiummetal does not plate out on the negative electrode during recharge ofthe cell. Lithium metal can cause cycling problems as well as safetyconcerns due to the reactivity of the lithium metal. To achieve thedesired high energy for the cell, the negative electrode structure canbe made thicker so that the negative electrode can provide theappropriate capacity in view of very high positive electrode capacities.

The high energy batteries described herein can have a negative electrodeformed, for example, with conventional lithium intercalating carbonmaterials. Suitable negative electrode active materials include, forexample, lithium intercalating carbons, some metal alloys, some siliconmaterials and some metal oxides. A separator is placed between thepositive electrode and the negative electrode. The electrode stack iscontacted with an electrolyte comprising lithium ions and generally anon-aqueous liquid. The electrode stack and electrolyte are sealedwithin a suitable container.

The nature of the negative electrode intercalation material influencesthe resulting voltage of the battery since the voltage is the differencebetween the half cell potentials at the cathode and anode. Suitablenegative electrode lithium intercalation compositions can include, forexample, graphite, synthetic graphite, hard carbon, mesophase carbon,appropriate carbon blacks, coke, fullerenes, niobium pentoxide,intermetallic alloys, silicon alloys, tin alloys, silicon, titaniumoxide, tin oxide, and lithium titanium oxide, such as Li_(x)TiO₂,0.5<x≦1 or Li_(1+x)Ti_(2−x)O₄, 0≦x≦⅓. Hard carbon suitable for use innegative electrodes is described further in U.S. patent application2003/0157014A to Wang et al., entitled “Pyrolyzed Hard Carbon Material,Preparation and its Applications,” incorporated herein by reference.Alloy based anodes are described further, for example, in U.S. Pat. No.6,730,429 to Thackeray et al, entitled “Intermetallic NegativeElectrodes for Non-Aqueous Lithium Cells and Batteries,” published U.S.patent application 2007/0148544A1 to Le, entitled “Silicon-ContainingAlloys Useful as Electrodes for Lithium-Ion Batteries,” and U.S. Pat.No. 7,229,717 to Yamaguchi et al., entitled “Anode Active Material andBattery Using it,” all three of which are incorporated herein byreference. The metal alloys can be combined with intercalation carbonsand/or conductive carbon. The negative electrode active materials can becombined with a polymer binder and associated with a current collectorto form the negative electrode. Similarly, other appropriateelectroactive negative electrode compositions can be used that provideappropriate discharge voltages with desired cycling capability.Additional negative electrode materials are described in copendingprovisional patent applications Ser. No. 61/002,619 to Kumar, entitled“Inter-metallic Compositions, Negative Electrodes With Inter-MetallicCompositions and Batteries,” and Ser. No. 61/125,476 to Kumar et al.,entitled “Lithium Ion Batteries With Particular Negative ElectrodeCompositions,” both of which are incorporated herein by reference. Insome embodiments, the negative electrodes can have a thickness on eachside of the current collector following compression of the anodematerial from 65 microns to 200 microns and in further embodiments from75 microns to 150 microns. In some embodiments, the anode has a densityof from about 1.5 to 1.7 g/mL. A person of ordinary skill in the artwill recognize that additional ranges of electrode thickness within theexplicit ranges above are contemplated and are within the presentdisclosure.

The positive electrode active compositions and negative electrode activecompositions generally are powder compositions that are held together inthe corresponding electrode with a polymer binder. The binder providesionic conductivity to the active particles when in contact with theelectrolyte. Suitable polymer binders include, for example,polyvinylidine fluoride (PVDF), polyethylene oxide, polyethylene,polypropylene, polytetrafluoroethylene, polyacrylates, rubbers, e.g.ethylene-propylene-diene monomer (EPDM) rubber or styrene butadienerubber (SBR), copolymers thereof and mixtures thereof. The positiveelectrode active material loading in the binder can be large, such asgreater than about 80 weight percent. These high loadings of positiveelectrode active material powders within the positive electrode can beformed with a more desirable and reproducible degree of mechanicalstability using polymers with a high molecular weight. In particular, insome embodiments, PVDF polymer binders have an average molecular weightof at least about 800,000 atomic mass units (AMU), in furtherembodiments at least about 850,000 AMU, in further embodiments at leastabout 900,000 AMU and in additional embodiments from about 1,000,000 AMUto 5,000,000 AMU. A person of ordinary skill in the art will recognizethat additional ranges of composition within the explicit ranges aboveare contemplated and are within the present disclosure. To form theelectrode, the powders can be blended with the polymer in a suitableliquid, such as a solvent for the polymer. The resulting paste can bepressed into the electrode structure.

The positive electrode composition, and possibly the negative electrodecomposition, generally also comprises an electrically conductive powderdistinct from the electroactive composition. Suitable supplementalelectrically conductive powders include, for example, graphite, carbonblack, metal powders, such as silver powders, metal fibers, such asstainless steel fibers, and the like, and combinations thereof.

The electrode generally is associated with an electrically conductivecurrent collector to facilitate the flow of electrons between theelectrode and an exterior circuit. The current collector can comprisemetal, such as a metal foil, a metal grid or screen, or expanded metal.Expanded metal current collectors refer to metal grids with a greaterthickness such that a greater amount of electrode material is placedwithin the metal grid. In some embodiments, the current collector can beformed from nickel, aluminum, stainless steel, copper or the like. Theelectrode material can be cast in contact with the current collector.For example, in some embodiments, the electrode material in contact withthe current collector foil or other structure can be subjected to apressure from about 2 to about 10 kg/cm² (kilograms per squarecentimeter). The pressed structure can be dried, for example in an oven,to remove the solvent from the electrode. Metal foils can be used ascurrent collectors. For example, copper foils can be used as currentcollectors for negative electrodes and aluminum foil can be used aspositive electrode current collectors. Pastes or slurries of the cathodematerials can be coated onto both sides of the foil. Then, theelectrodes can be pressed using calendering rolls, a press with a die orother suitable processing apparatus to compress the electrodes to adesired thickness. The positive electrodes can have an active materialparticle loading on each side of the current collector from 20 mg/cm² to50 mg/cm². The positive electrodes can have a density of at least 2.5grams per milliliter (g/mL), in further embodiments at least about 2.8g/ml and in additional embodiments from about 3.0 g/mL to about 3.5g/mL. A person of ordinary skill in the art will recognize thatadditional ranges of active material loading within the explicit rangeabove are contemplated and are within the present disclosure.

The separator is located between the positive electrode and the negativeelectrode. The separator is electrically insulating while providing forat least selected ion conduction between the two electrodes. A varietyof materials can be used as separators. For example, glass fibers formedinto a porous mat can be used as a separator. Commercial separatormaterials are generally formed from polymers, such as polyethyleneand/or polypropylene that are porous sheets that provide for ionicconduction. Commercial polymer separators include, for example, theCelgard® line of separator material from Hoechst Celanese, Charlotte,N.C. Suitable separator materials include, for example, 12 micron to 40micron thick trilayer polypropylene-polyethylene-polypropylene sheets,such as Celgard® M824, which has a thickness of 12 microns. Also,ceramic-polymer composite materials have been developed for separatorapplications. These composite separators can be stable at highertemperatures, and the composite materials can significantly reduce thefire risk. The polymer-ceramic composites for separator materials aredescribed further in U.S. patent application 2005/0031942A to Hennige etal., entitled “Electric Separator, Method for Producing the Same and theUse Thereof,” incorporated herein by reference. Polymer-ceramiccomposites for lithium ion battery separators are sold under thetrademark Separion® by Evonik Industries, Germany.

Electrolytes for lithium ion batteries can comprise one or more selectedlithium salts. Appropriate lithium salts generally have inert anions.Suitable lithium salts include, for example, lithiumhexafluorophosphate, lithium hexafluoroarsenate, lithiumbis(trifluoromethyl sulfonyl imide), lithium trifluoromethane sulfonate,lithium tris(trifluoromethyl sulfonyl)methide, lithiumtetrafluoroborate, lithium perchlorate, lithium tetrachloroaluminate,lithium chloride and combinations thereof Traditionally, the electrolytecomprises a 1 M concentration of the lithium salts. In some embodiments,conventional electrolyte compositions can be used, such as a 1 molarsolution of LiPF₆ in a blend of ethylene carbonate and dimethylcarbonateat a 1 to 1 by volume ratio. In some particular embodiments, solidelectrolyte can be used, which generally also functions as the separatorfor electrodes. Solid electrolytes are described further, for example,in U.S. Pat. No. 7,273,682 to Park et al., entitled “Solid Electrolyte,Method for Preparing the Same, and Battery Using the Same,” incorporatedherein by reference.

For lithium ion batteries of interest, a non-aqueous liquid is generallyused to dissolve the lithium salt(s). The solvent is generally inert anddoes not dissolve the electroactive materials. Appropriate solventsinclude, for example, propylene carbonate, dimethyl carbonate, diethylcarbonate, 2-methyl tetrahydrofuran, dioxolane, tetrahydrofuran, methylethyl carbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile,formamide, dimethyl formamide, triglyme(tri(ethylene glycol)dimethylether), diglyme(diethylene glycol dimethyl ether), DME (glyme or1,2-dimethyloxyethane or ethylene glycol dimethyl ether), nitromethaneand mixtures thereof.

The electrodes described herein can be incorporated into variouscommercial cell designs. For example, the cathode compositions can beused for prismatic shaped cells, wound cylindrical cells, coin cells,pouch cells or other reasonable cell shapes. The testing in the Examplesis performed using coin cells and pouch cells. The cells can comprise asingle positive electrode structure or a stacked structure with aplurality of positive electrodes assembled in parallel and/or serieselectrical connection(s). In particular, the battery can comprise astack of alternating positive electrodes and negative electrodes withseparators between them. Generally, the plurality of electrodes isconnected in parallel to increase the current at the voltage establishedby a pair of a positive electrode and a negative electrode. While thepositive electrode active materials can be used in batteries forprimary, or single charge use, the resulting batteries generally havedesirable cycling properties for secondary battery use over multiplecycling of the cells.

In some embodiments, the positive electrode and negative electrode canbe stacked with the separator between them, and the resulting stackedstructure can be rolled into a cylindrical or prismatic configuration toform the battery structure. Appropriate electrically conductive tabs canbe welded or the like to the current collectors and the resultingjellyroll structure can be placed into a metal canister or polymerpackage, with the negative tab and positive tab welded to appropriateexternal contacts. Electrolyte is added to the canister, and thecanister or package is sealed to complete the battery.

Some presently used rechargeable commercial cells include, for example,the cylindrical 18650 cells (18 mm in diameter and 65 mm long) and 26700cells (26 mm in diameter and 70 mm long), although other cell sizes canbe used. Cylindrical cell is a widely used battery packaging format. Thecylindrical shape of the cell has the ability to withstand high internaland external pressure. Additionally, cylindrical cells can have aventing mechanism to release excessive internal pressure. Because of itscylindrical shape and fixed sizes, however, cylindrical battery cellgenerally has poor space utilization and has to be designed aroundavailable cell sizes. In a cylindrical cell, the electrodes andseparators can be made into long thin sheets and rolled into a spiral orjelly-roll shape optionally around a rod shaped positive terminal.Alternatively, the electrodes can be wound onto a flat mandrel toprovide flattened shaped that can fit inside a prismatic case to make aprismatic cell. Electrodes can alternatively or additionally be stackedwithin a prismatic shaped cell.

Prismatic cells come in various sizes that can be custom-made to meetdifferent size and energy demands. One version of a prismatic cell isreferred to as a pouch cell, which generally has a heat-sealable foil toenclose rolled or stacked electrodes and separators as an alternative toa metal can. Pouch cell battery format generally allows tailoring toexact cell dimensions and makes the most efficient use of availablespace and can sometimes achieve a packaging efficiency of 90 to 95percent, the highest among battery packs. Because of the absence of ametal can, the pouch cells are generally light. Prismatic and pouch cellformats can contains a plurality of positive electrode sheets andnegative electrode sheets that are sandwiched together in layers withseparators in-between.

To achieve the very high energies for the cells described herein, thepositive electrode designs generally comprise the high capacity cathodeelectroactive compositions described above. However, the positiveelectrodes generally also involve a high loading of the electroactivematerials into the electrode with corresponding decreases inelectrically conductive powders and binder. The electrode should haveappropriate cohesiveness at the high particle loadings. This can beaccomplished with appropriate selection of the polymer binder, such asusing a high molecular weight binder and/or a rubber polymer.

In some particular embodiments, the positive electrode can comprise fromabout 90 to about 99 weight percent active material, in furtherembodiments from about 92 to 98 weight percent, in additionalembodiments from about 92. to about 97.5 weight percent and in otherembodiments from about 92.5 to about 97 weight percent active material.Similarly, the positive electrode can comprise from about 0.1 to about 8weight percent supplemental electrically conductive agent, in furtherembodiments from about 0.5 to about 6 weight percent electricallyconductive agent and in additional embodiments form about 1 to about 5weight percent electrically conductive agent. In addition, the positiveelectrode can comprise from about 0.5 to about 8 weight percent polymerbinder, in further embodiments from about 1.0 to about 6 weight percentpolymer binder and in additional embodiments form about 1.5 to about 5weight percent polymer binder. A person of ordinary skill in the artwill recognize that additional ranges of amounts of positive electrodecompositions within the explicit ranges above are contemplated and arewithin the present disclosure. Suitable conductive agents include, forexample, graphite powder, carbon black, combinations thereof and thelike.

The batteries described herein are formed with active materials thatprovide for a high degree of safety. Commercial lithium ion batterieshave suffered from safety concerns due to occasions of batteriescatching fire. In contrast with commercial cells having relatively highenergy capacity, the cells described herein are based on materials thatdo not have corresponding instabilities so that the present cells do notexhibit thermal run away. If the cells described herein are heated, theydo not spontaneously react to catch fire. Relatively high energycommercial lithium ion cells exhibit thermal runaway in which the heatedcells undergo reaction and catch fire. Thus, the cells herein provideimproved energy capacity as well as providing increased safety duringuse.

Improved Cell Performance

As noted above, the positive electrode electroactive materials can havea high energy capacity, generally at least about 200 milliamperehours/gram (mAh/g), in some embodiments at least about 225 mAh/g, and infurther embodiments at least about 250 mAh/g, with good cycling. Withthe cells designs described herein, the batteries can have a totalenergy density of at least about 240 Watt-hours/kilogram (Wh/kg), infurther embodiments from about 250 to 550 Wh/kg, in some embodimentsfrom about 280 to 500 Wh/kg and in further embodiments from about 300 to450 Wh/kg, in a desired shape and sized battery. Alternatively, whenmeasured in volumetric terms, the batteries can have a total volumetricenergy density of at least about 550 Watt-hours/liter (Wh/l), in furtherembodiments from about 650 to 1150 Wh/l, in some embodiments from about675 to 1050 Wh/l and in further embodiments from about 700 to 1000 Wh/l,in a desired shape and sized battery. The volume of a battery can beevaluated for example as the cross sectional area of the cell canistertimes the length of the cell canister, or as the length times the widthand the thickness of the battery cell. A person of ordinary skill in theart will recognize that additional ranges of battery capacities withinthe explicit ranges above are contemplated and are within the presentdisclosure.

In contrast with the present cell designs, U.S. Pat. Nos. 7,201,997 and7,166,385 both to Ishida et al., both incorporated herein by reference,describe details involving electrode thickness versus energy density,cycle life and rate capability in the context of lithium ion batterieswith high energy density active materials. Both anode and cathodethickness is varied from 60 to 360 micron and the data shows significantdecrease in cycle life and rate capability as electrode thicknessincrease. These cell designs incorporated conventional positiveelectrode active materials. These patents do not report performanceslevels achieved herein. In the cells described herein, the positiveelectrodes can be thinner while providing high energies through the useof higher capacity active materials as well as using higher loadings ofactive materials.

In general, various similar testing procedures can be used to evaluatethe battery performance. A specific testing procedure is described forthe evaluation of the performance values described herein. The testingprocedure is described in more detail in the examples below.Specifically, the battery can be cycled between 4.6 volts and 2.0 voltsat room temperature, although other ranges can be used withcorrespondingly different results. The evaluation over the range from4.6 volts to 2.0 volts is desirable for commercial use since thebatteries generally have stable cycling over this voltage range. For thefirst three cycles, a battery is discharged at a rate of C/10 toestablish irreversible capacity loss. The battery is then cycled forthree cycles at C/5. For cycle 7 and beyond, the battery is cycled at arate of C/3, which is a reasonable testing rate for medium currentapplications. Again, the notation C/x implies that the battery isdischarged at a rate to fully discharge the battery to the selectedlower voltage cut off in x hours. The battery capacity generally dependssignificantly on the discharge rate, with lose of capacity as thedischarge rate increases.

In some embodiments, the positive electrode active material has aspecific capacity during the tenth cycle at a discharge rate of C/3 ofat least about 235 milliamp hours per gram (mAh/g), in additionalembodiments from about 240 mAh/g to about 310 mAh/g, in furtherembodiments from about 245 mAh/g to about 300 mAh/g and in otherembodiment from about 250 mAh/g to about 290 mAh/g. Additionally, the20^(th) cycle discharge capacity of the material is at least about 98%,and in further embodiments 98.5% of the 5^(th) cycle discharge capacity,cycled at a discharge rate of C/3. It has been found that the firstcycle irreversible capacity loss for metal fluoride coated electroactivematerials can be decreased at least about 25%, and in furtherembodiments from about 30% to about 60% relative to the equivalentperformance of the uncoated materials. The tap density of the materialcan be at least about 1.8 g/mL, in further embodiments from about 2 toabout 3.5 g/mL and in additional embodiments from about 2.05 to about2.75 g/mL. High tap density translates into high overall capacity of abattery given a fixed volume. A person of ordinary skill in the art willrecognize that additional ranges of specific capacity and tap densityand of decreases in irreversible capacity loss are contemplated and arewithin the present disclosure. For fixed volume applications such asbatteries for electronic devices, high tap density therefore highoverall capacity of the battery is of particular significance.

Generally, tap density is the apparent powder density obtained understated conditions of tapping. The apparent density of a powder dependson how closely individual particles of the powder are pack together. Theapparent density is affected not only by the true density of the solids,but by the particle size distribution, particle shape and cohesiveness.Handling or vibration of powdered material can overcome some of thecohesive forces and allow particles to move relative to one another sosmaller particles can work their way into the spaces between the largerparticles. Consequently, the total volume occupied by the powderdecreases and its density increases. Ultimately no further naturalparticle packing can be measured without the addition of pressure and anupper limit of particle packing has been achieved. While electrodes areformed with the addition of pressure, a reasonably amount of pressure isonly effective to form a certain packing density of the electroactivematerials in the battery electrode. The actual density in the electrodegenerally relates to the tap density measured for a powder so that thetap density measurements are predictive of the packing density in abattery electrode with a higher tap density corresponding to a higherpacking density in the battery electrode.

EXAMPLES

Batteries of different packaging (for example, coin cell versus pouchcell) were constructed and tested in Examples 1-3. The resultingbatteries were tested with a Maccor cycle tester to obtaincharge-discharge curve and cycling stability over a number of cycles.

Example 1 Cathode Capacity Determined from Coin Cell BatteryMeasurements

This example demonstrates the high energy density that is available froma battery having a positive electrode formed with high loading of anactive material. The active material has a high energy capacity as wellas particle properties that provide for a high loading into theelectrode.

The positive electrode was formed with cathode powders having thechemical formula Li[Li_(0.2)Ni_(0.175)Co_(0.10)Mn_(0.525)]O_(2.0) and asurface coating of aluminum fluoride. The material was synthesized asdescribed in the example of the '735 application. Cathode powders weremixed with conductive carbon in a jar mill for a few hours. Theresulting powder was mixed with PVDF and N-methyl pyrrolidone (NMP)solution using a magnetic stirrer to faun an homogeneous slurry. ThePVDF had an average molecular weight of 1 million atomic mass unit(AMU). The slurry was coated on an aluminum foil to desired thicknessand then vacuum dried. The dried coated foil was compressed to desiredthickness, and electrodes were punched out of the coated foil forfabricating coin cell batteries. The electrode thus formed comprises94.25 weight % cathode powder, 3 weight % conductive carbon and 2.75weight % PVDF binder. The electrode had an active cathode materialloading level of 18.1 mg/cm² and a density of 3.0 g/mL. In general ifequivalent electroactive powders and electrically conductive carbon wasprocessed with a PVDF polymer having a molecular weight significantlylower than 1 million AMU, the resulting structure had poor performanceand difficulties for assembly related to insufficient adhesion andcohesion of the electrode materials.

Coin cell batteries were assembled in argon filled dry box using 1MLiPF₆. Lithium foil was used as the negative electrode and a commercialseparator material was placed between the positive and negativeelectrodes. The battery cells were cycled at room temperature at a C/10rate. i.e., a rate the battery cell is discharged in 10 hours. Theperformance of the battery cell was tested with a Maccor™ battery celltester. FIG. 2 shows the charge and discharge capacities of the firstcharge-discharge cycle of the coin cell battery. As shown in FIG. 2, thecathode material exhibited an initial charge capacity of 310 mAh/g and adischarge capacity of 277 mAh/g. The battery cells were cycled between4.6V to 2.0 V at various rates. FIG. 3 shows cycling stability of thebattery cell measured up to 50 cycles. For the first three cycles, thebattery is discharged at a rate of C/10 to establish irreversiblecapacity loss. The battery is then cycled for three cycles at C/5. Forcycle 7 and beyond, the battery is cycled at a rate of C/3, which is areasonable testing rate for medium current applications. Again, thenotation C/x implies that the battery is discharged at a rate to fullydischarge the battery to the selected lower cutoff in the voltage in xhours.

Example 2 Cathode Capacity Determined from Another Coin Cell BatteryMeasurements

This example demonstrates the high energy capacity that is available ina coin cell battery with an anode comprising a lithium intercalationmaterial. The coin cell has a positive electrode formed with highloading of an active cathode material.

Positive electrode was formed using cathode powders having the chemicalformula Li[Li_(0.2)N_(0.175)Co_(0.10)Mn_(0.525)]O_(2.0) and a surfacecoating of aluminum fluoride. Cathode powders were mixed with conductivecarbon in a jar mill for a few hours. The resulting powder was mixedwith PVDF and N-methyl pyrrolidone (NMP) solution using a magneticstirrer to form homogeneous slurry. The PVDF used has an averagemolecular weight of 1 million AMU. The slurry was coated on an aluminumfoil to desired thickness and then vacuum dried. The dried coated foilwas compressed to desired thickness and electrodes were punched out ofthe coated foil for fabricating the coin cell batteries. The electrodethus formed comprises 94.25 weight % cathode powder, 3 weight %conductive carbon and 2.75 weight % PVDF binder. The electrode has anactive cathode material loading level of 20.2 mg/cm².

Coin cell batteries were assembled in argon filled dry box using 1MLiPF₆. A graphitic carbon coated onto copper foil was used as thenegative electrode, and a trilayer(polypropylene/polyethylene/polypropylene) micro-porous separator (2320from Celgard, LLC, NC, USA) was placed between the positive and thenegative electrodes. The battery cells were cycled at room temperatureat a C/10 rate. i.e. a rate at which the battery cell is discharged andcharged in 10 hours. The performance of the cell battery was tested witha Maccor™ battery cell tester. FIG. 4 shows charge-discharge capacity ofthe coin cell batteries between 4.55V charge and 2.5V discharge cut-off.As shown in FIG. 4, the cathode material exhibited a discharge capacityof 260 mAh/g over the cycle range shown, in which the discharge rateswere varied for the later cycles as described in Example 1.

Example 3 Cathode Capacity Determined from Pouch Cell BatteryMeasurements

This example demonstrates the high energy capacity that is available ina pouch cell battery formed with high loading of an active cathodematerial. A pouch cell battery with dimensions 190 mm×95 mm×8 mm(volume=0.144 L) was constructed and tested following the sameconstruction and testing approaches outlined in example 2, withadaptations to suite the pouch cell battery with a stack of electrodesseparated with separators. The positive electrodes are connected inparallel, and the negative electrodes are similarly connected inparallel. FIG. 5 a shows a photo of the front of the pouch cell battery.FIG. 5 b shows a photo of the side of the pouch cell battery. FIG. 5 cshows a discharge curve of the pouch cell battery having 23 Ah andenergy density of 250 Wh/kg.

Data presented in Examples 1 and 2 above demonstrated cathode capacityof 277 mAh/g using a lithium anode and cathode capacity of 260 mAh/gusing a carbon anode at C/10 cycling rates, respectively. Positiveelectrodes discussed herein were shown to support a 25 Ampere-hourpractical battery design, and the data is shown in tables 1 and 2. Thevolumetric energy density of the batteries ranged from 550-650 Wh/l at aC/10 cycling rate. As a comparison, performance results using commercialLiCoO₂ is shown yielding 425-525 Wh/l at a C/10 cycling rate whenemployed with the same electrode porosity as the cathodes in theExamples.

TABLE 1 Binder Cathode Volumetric Energy Density (Wh/l)^(a) BMW, kDaActive % Li[Li_(0.2)Ni_(0.175)Co_(0.10)Mn_(0.525)]O_(2.0) LiCoO₂ 30080-88 350-450 225-325 600 89-92 475-525 350-400 1000 93-97 550-650425-525 ^(a)energy density is measure with 25 Ah cell cycled at C/10cycling rate

TABLE 2 Binder Cathode Discharge Energy Density (Wh/kg) BMW, kDa Active% Li[Li_(0.2)Ni_(0.175)Co_(0.10)Mn_(0.525)]O_(2.0) LiCoO₂ 300 80-88140-170 120-140 600 89-92 175-235 150-170 1000 93-97 240-320 180-210

The embodiments above are intended to be illustrative and not limiting.Additional embodiments are within the claims. In addition, although thepresent invention has been described with reference to particularembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention. Any incorporation by reference of documents above islimited such that no subject matter is incorporated that is contrary tothe explicit disclosure herein.

What is claimed is:
 1. A lithium ion secondary battery comprising a positive electrode comprising a first lithium rich lithium intercalation composition, which is lithium rich relative to a LiMO₂ reference composition with M representing non-lithium metal elements, a negative electrode comprising a second lithium intercalating composition, and a separator between the positive electrode and the negative electrode, wherein the positive electrode comprises at least about 92 weight percent of the first lithium rich lithium intercalation composition, about 0.1 to 5 weight percent electrically conductive agents, about 0.5 to 7.9 weight percent polymer binder comprising polyvinylidene fluoride (PVDF), and a first current collector; wherein the polymer binder has an average molecular weight of at least about 800,000 atomic mass units; wherein the density of the positive electrode is at least about 2.5 g/ml; wherein the first lithium rich lithium intercalation composition has a specific capacity of at least about 200 mAh/g when discharged from 4.6V to 2.0V at a rate of C/3 and a 20th cycle discharge capacity that is at least about 98% of the 5th cycle discharge capacity when cycled between 4.6V to 2.0V at a discharge rate of C/3; and wherein the first lithium intercalation composition is approximately represented by a formula of xLiMO₂.(1−x)Li₂M′O₃ where M is one or more trivalent metal ions with at least one metal being Mn⁺³, Co⁺³, or Ni⁺³ and M′ represents one or more metal ions having an average valence of +4 and 0<x<1, a formula Li_(1+x)Ni_(α)Mn_(β)Co_(γ)M″_(δ)O_(2−z/2)F_(z) where x ranges from about 0.05 to about 0.25, α ranges from about 0.1 to about 0.4, β ranges from about 0.4 to about 0.65, γ ranges from about 0.05 to about 0.3, δ ranges from about 0 to about 0.1 and z ranges from about 0 to about 0.1 and where M″ is Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb or combinations thereof, or both.
 2. The lithium ion secondary battery of claim 1 wherein the battery has a discharge energy density of at least about 240 Wh/kg when discharged from 4.6V to 2.0V.
 3. The lithium ion secondary battery of claim 1 wherein the first lithium intercalation composition is represented by a formula of xLiMO₂.(1-x)Li₂M′O₃ where M is one or more trivalent metal ion with at least one metal ion being Mn⁺³, Co⁺³, or Ni⁺³ and M′ represents one or more metal ions having an average valance of +4 and 0<x<1.
 4. The lithium ion secondary battery of claim 1 wherein the first lithium intercalation composition comprises from about 0.1 mole percent to about 10 mole percent metal fluoride as a coating.
 5. The lithium ion secondary battery of claim 4 wherein the metal fluoride comprises AlF₃.
 6. The lithium ion secondary battery of claim 1 further comprising a second current collector and wherein the negative electrode has a thickness from about 65 microns to about 200 microns on a single side of the second current collector.
 7. The lithium ion secondary battery of claim 1 wherein the battery has a discharge energy density of at least about 250 Wh/kg to 550 Wh/kg, and an active material loading on each side of the first current collector from about 20 mg/cm² to about 50 mg/cm².
 8. The lithium ion secondary battery of claim 1 wherein the battery has a volumetric discharge energy density of at least about 550 Wh/l.
 9. The lithium ion secondary battery of claim 1 wherein the first lithium intercalation composition is represented by a formula Li_(1+x)Ni_(α)Mn_(β)Co_(γ)O₂, where x ranges from about 0.05 to about 0.25, α ranges from about 0.1 to about 0.4, β ranges from about 0.4 to about 0.65, and γ ranges from about 0.05 to about 0.3.
 10. The lithium ion secondary battery of claim 9 wherein the battery comprises a plurality of electrodes with each polarity separated by separators within a casing and wherein electrodes and separators are stacked, jelly-rolled, or folded inside the casing.
 11. The lithium ion secondary battery of claim 10 wherein the casing comprises a polymeric film, a metallic foil, or a combination thereof, and wherein the casing is prismatic in shape.
 12. The lithium ion secondary battery of claim 1 wherein the first lithium intercalation composition is represented by a formula Li_(1+x)Ni_(α)Mn_(β)Co_(γ)M″_(δ)O_(2−z/2)F_(z), where x ranges from about 0.05 to about 0.25, α ranges from about 0.1 to about 0.4, β ranges from about 0.4 to about 0.65, γ ranges from about 0.05 to about 0.3, δ ranges from about 0 to about 0.1 and z ranges from about 0 to about 0.1, and where M″ is Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb or combinations thereof.
 13. The lithium ion secondary battery of claim 1 wherein the negative electrode comprises graphite, synthetic graphite, hard carbon, graphite coated metal foil, coke or a combination thereof.
 14. The lithium ion secondary battery of claim 1 wherein the separator comprises polyethylene, polypropylene, ceramic-polymer composites, or a combination thereof.
 15. The lithium ion secondary battery of claim 1 wherein the separator comprises a polyethylene-polypropylene-polyethylene tri-layer membrane.
 16. The lithium ion secondary battery of claim 1 wherein the electrically conductive material comprises graphite, carbon black, metal powders, metal fibers, or a combination thereof.
 17. The lithium ion secondary battery of claim 1 wherein the positive electrode active material has a specific capacity of at least about 225 mAh/g at the 10^(th) cycle when discharged from 4.6V.
 18. The lithium ion secondary battery of claim 1 wherein the positive electrode comprises from about 1.0 to about 6 weight percent polymer binder.
 19. The lithium ion secondary battery of claim 1 wherein the polymer binder has an average molecular weight from about 1,000,000 atomic mass units to 5,000,000 atomic mass units. 